The French side were worth their three points at the Georgios Karaiskakis Stadium after enjoying the better of the chances in a game that lacked fluidity.
Souleymane Diawarra went close early on before Kevin Mirallas had an effort for the hosts. Benoit Cheyrou’s header landed on the roof of the net after 35 minutes before Loic Remy struck the post.
Gonzalez converted Jeremy Morel’s centre after six minutes of the second half to score the only goal of the game and despite substitute Rod Fanni's dismissal in the 90th minute for a lunge on Avraam Papadopoulos, it was a satisfactory night for Didier Deschamps's side.
Both sides looked disjointed during the opening 20 minutes of a tense first half. Understandably Olympiacos, who are yet to play a competitive game in this season's Greek Super League, looked very unsettled and could have been a goal down after two minutes.
Cheyrou’s inswinging corner from the right found the head of Diawarra who was standing six yards from goal. The defender appeared to get ahead of the ball and could only direct his header over the bar.
Marseille continued to shade the game marginally as their passing proved a little slicker than the hosts.
Cheyrou was the next to have an effort on goal as he received the ball deep in the Olympiacos half, and under no pressure at all elected to shoot from 30 yards. The effort was struck superbly well but the distance it was hit from allowed the keeper to see it early and make the save.
On the 20 minute mark, Olympiacos had their first effort of the match. Mirallas ventured down the left and checked his run beat and two men before rifling a fierce effort towards goal from the edge of the penalty area. Unfortunately for the Belgian international, the ball flew straight into the hands of Steve Mandanda.
The striker had another effort just moments later as Ljubomir Fejsa burst down the right and cut the ball back into the path of Mirallas, who could only drag his effort wide from 10 yards.
Olympiacos slowly grew into the game which made for a more even final 20 minutes of the opening half.
The best chance of the opening 45 minutes fell to Remy just eight minutes before the interval.
Cheyrou intercepted a pass and sent the striker down the left with an excellent through ball. Remy cut inside of Papadopoulos as he burst into the box before rattling an effort off the near post from eight yards.
After just six minutes of the second half Marseille took the lead. Morel flew down the left flank and skipped past the challenge of Mellberg before crossing from the byline. Gonzalez timed his run perfectly to beat the covering defender to the ball and finish from four yards.
The hosts, who boasted an impressive home record during last season, looked to get back into the game as they pressed their opponents high up the pitch. Ernesto Valverde also introduced a number of attacking substitutes, but with every one attacking change Olympiacos made, Deschamps countered it with a defensive change of his own.
The Greek side shaded possession in the second half but lacked creativity when going forward. Their only real chance of taking anything from the game came in the 75th minute when Vasilis Torosidis created some space on the right touchline and whipped an inviting cross into the penalty area. Substitute Rafik Djebbour strode forward to meet the ball but could only volley over from 15 yards. In hindsight, he may have been better attempting to go at the ball with his head.
Djamel Abdoun later half-volleyed wide of the goal from the edge of the penalty area as time ran out for the hosts.
Marseille rarely looked like conceding and the only dampener on a pretty solid performance came in the 90th minute when substitute Fanni was shown a straight red card for a studs-up lunge on Papadopoulos.